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Water Hammer Problem

We bought a home with the sprinkler system installed by the previous owner. The local water pressure is 120 psi. One of the existing valves blew apart after 10 years of service. I replaced the old valves with RainBird 075-ASVF rated at 150psi. But several lines have a significant water hammer when the valves shut off. I tried using a pressure regulator to 80 psi, but then there is not enough pressure to feed the existing circuits. I removed the regulator and tried varying the sequence of the circuits with little improvement. Water hammer arrestors would have to be very large to handle this pressure. Are there any valves that can handle this pressure with a gradual close? Are there any other ways to reduce the water hammer without redoing the whole system [?]

Oh man water hammer. It's one of my worst nightmares. I've tried everything. But you did mention the only way I've ever been able to cure it. By installing slow closing valves. Since you have such a high water pressure and you're using anti-syphon valves, I recommend you go to an all brass valve. A brass anti-syphon valve body with Superior brand valve adapters. It's the 800 series. They close slow and can easily handle the pressure. It's an expensive fix and no guarantee it will completly cure the problem but no doubt it will help. I hope the other guys chime in with ideas. I'd like to hear them. Also I read a water hammer article recently. I'll see if I can find it and I'll post a link for you.

Can't remember the name of the valve (thinkin' it's a Watts Regulator Brand Valve) but it has a bypass that regulates the pressure that activates the diaphragm (Not a pressure regulating valve). In a since, it would reduce the pressure to a more manageable amount inside the valve to eliminate the water hammer (how fast and slow the diaphragm closes). I will have to dig around and find it again, and It may be too expensive of a cure.

Let me throw out an idea. I've never tried this or heard of it. Let me know if where the idea goes wrong. I believe water hammer is caused by the amount of flow and speed of the water. What if I increased the pipe size before the manifold. For example, the manifold and main line leading to the manifold is 3/4 inch. What if I put a piece of 1" pipe in the mainline before the manifold. Let's say? 6 feet? Or even 1 1/4 inch. Would this slow the flow down enough to stop water hammer?

I don't think there's much effort in manufacturing valves to close slowly on high supply pressures. Easier to correctly design a system from the start. Reduce the flow on the hammering zones, and the hammer will also be reduced.

After reading this article again, I'm thinking that's where I got the above idea from. I guess this is how senility starts. =) The article has some interesting solutions. --
http://www.irrigationtutorials.com/waterhammer.htm

Thank you for the time and effort you invested in my problem. I had already found this article, and tried varying the sequence of the circuits; I think I will try this again. I'm trying to avoid digging up the system to increase the pipe size or add more circuits, though that's probably the surest solution. Your earlier response recommended using Superior Brand valves. I found their website and they advertise slow closing on their valves. Does your experience with them under high line pressure verify their claims? I'd be willing to try them if you know they work well. Thanks again.

They do function well under high pressure. They do close slowly as advertized. I can't promise it will completly cure the problem but it might. I'd say 75% of the systems I've converted to the 800 series were completly cured. The other 25% there was definite decrease in water hammer. I do live in a city where the pressure varies from 50 pounds to 130 depending on location. I suggest you tighten down the screws around the valve. Your high pressure will cause them to leak in a few years if you don't. Good luck!